1. Field of the Invention
This invention relates to catalysts useful for polymerization of alpha-olefins and more particularly, to a titanium halide catalytic component supported on magnesium compounds and a catalyst system comprising such a supported catalytic component.
2. Description of the Prior Art
Catalysts on magnesium-containing carriers which have high catalytic activity and good stereospecificity have been developed and are known to be suitable for vapor phase polymerization of alpha-olefins because of their advantages that the treatment of the catalyst residue in produced polymer is easy and that removal of App components is not necessary.
In order to ensure good operability, the catalysts for the vapor phase polymerization of alpha-olefins are further required to have a good shape of particles with a narrow distribution of particle size, a good shatter resistance and a high bulk density. One of techniques for obtaining a controlled shape of catalyst particles is described in Japanese Laid-open Patent Application No. 63-54,405 wherein magnesium compounds are dissolved in an alcohol in the presence of carbon dioxide and treated with a mixture of a titanium halide and an organosilane to cause precipitation, to which a cyclic ether compound is added for re-dissolution and recrystallization, thereby obtaining a carrier with a good shape, and the carrier is activated to provide a catalyst.
In the vapor phase polymerization of alpha-olefins wherein secondarily produced rubber components are not extracted in solvent as is different from the suspension polymerization, there are produced a number of copolymers. For the production of adhesive polymers having high rubber contents, it is necessary to keep good fluidity of polymer powder, which in turn requires the polymer powder having a large size. Accordingly, catalytic ingredients having a large particle size are required as bringing about such a large-sized powder.
In general, catalyst particles prepared from a solution by a precipitation method involve the inevitable drawback that although particles of the carrier are uniform with a sharp distribution of particle size, part of the particles is broken in a subsequent activation step. In addition, particles of a larger size are more liable to break. In Japanese Laid-open Patent Application No. 63-54,405, there is the problem that when the particle size is as large as 30.mu., the particles are broken in large amounts during the activation treatment such as with titanium halides, so that fine powder increases in amount.
In Japanese Laid-open Patent Application No. 63-54,405, there is described a method for preparing a catalytic component with a good shape wherein alkaline earth metal alcoholates are dissolved as an alcohol solution by the use of carbon dioxide and a silicone compound is used for the formation of a catalytic component, followed by complexing the alkaline earth metal such as magnesium by the use of tetrahydrofuran.
Many methods using silicon compounds for the formation of catalytic components have been attempted, but use of a boron compound instead of the silicon compound has never been disclosed up to now. In Japanese Laid-open Patent Application No. 63-277,204, use of a boron compound in combination with a silicon compound is set forth but the effect of the boron compound is not explained.
We have made intensive studies on an improved method for the preparation of a catalytic system of the type described before wherein the catalytic component is controlled to have small to large sizes and particularly, to have an appropriate shape and an appropriate size distribution especially in large particle size while keeping good polymerization properties such as high activity and high stereoregularity. As a result, it has been found that the breakage of the particles during the preparation process of the catalytic component is prevented thereby forming a well-shaped catalytic component having a sharp size distribution.
In the second aspect of the invention, we have found a method for producing a large-sized supported catalyst wherein a specific type of silane compound, e.g. an alkylsilane alkoxide, is used as a shape control agent at the time of precipitation from solution and wherein when a cyclic ether is added for recrystallization, an alcohol is added by which in the preparation of a catalytic component and, particularly, a particulate catalyst with a large size, the particles suffer little or only a slight degree of degradation during the treatment with titanium halides.
With regard to the third aspect of the invention, we have already proposed a method for producing a supported catalyst wherein a boron compound is used as a shape control agent at the time of precipitation from solution by which in the preparation of a catalytic component and, particularly, a particulate catalyst with a large size, the particles suffer little or only a slight degree of degradation during the treatment with titanium halide. Further studies have been made and, as a result, it has been found that a catalyst with a large size and a better crystal form can be prepared. The present invention is based on this finding.
With regard to the fourth aspect of the invention, we have found a process for preparing a large-sized catalyst of the supported type wherein a specific type of silane compound, i.e. an alkylsilane alkoxide, is used as a shape-controlling agent at the time of precipitation from solution and an alcohol is added to a recrystallization system to which a cyclic ether compound has been added, by which a catalytic ingredient is prepared and particularly, a large-sized catalyst is prepared without any breakage thereof during treatment with titanium halides or with the particles being broken only in small amounts, if any.